The means of supplying power to customers has changed drastically over the years. Early grid systems used local power generators to supply small networks with direct current (current being electrical flow) at a single voltage (electrical pressure), much like a simple flashlight where a battery powers a light. However, using direct current to transmit electrical power over long distances incurs more losses than using alternating current (current that alternately flows back and forth, towards and away from the power source). Also, transmitting electrical power at lower voltages and higher current over long distances incurs more losses than using higher voltages at lower current. Adoption of alternating current and long distance transmission of electricity at high voltage, together with advancements in transformer technology (transformers enable changes of voltages) unlocked voltage flexibility and economies of scale to allow power plants to grow and move further away from customers. Recently, there has been a dramatic increase in new and innovative grid participants (public, private and other entities that directly or indirectly generate energy, store energy, distribute energy, manage energy, aggregate energy, collect and provide information on energy, and/or perform any other energy related function or functions in front of customers' utility meters). Grid participants include, but are not limited to traditional electric utilities, energy generators, energy distributors, energy aggregators, and energy management companies.
Further, intermittent power generation systems (which preferably convert renewable energy sources, including the sun, wind, waves and others into electrical energy) have become popular as the price of oil and other conventional energy sources has increased. They are versatile and can be used at public or private properties, including residential, commercial or industrial properties. However, they usually provide direct current (so inverters must be used to connect to alternating current systems) and can cause unpredictable rapid fluctuations in electrical power generation (surges and lulls) due to unpredictable rapid fluctuations in environmental conditions, such as moving clouds, erratic changes in wind speed and direction, and changes in wave height and wave span. Unlike randomly dispersed electrical loads that are, in aggregate, similar and predictable across significant regions of a grid, intermittent power generation systems (such as photovoltaic (PV), wind, and other renewable energy systems) introduce wide ranging and instantly changing instabilities on localized segments of a grid, especially in areas where the grid is close to being saturated with connected intermittent power generation systems. Some utilities now restrict or even forbid additional connections of intermittent power generation systems to grid portions with high levels of existing connected intermittent power generation systems that are already saturated with power.
Of course, customers can go completely “off-grid” by using intermittent power generation systems that are not connected to the grid, together with energy storage devices (batteries) to store and discharge all the intermittent power produced from these stand-alone systems; however, these stand-alone systems require batteries with large amounts of storage capacity, making them very expensive. One solution to the problem of intermittent power related instabilities has been to reject intermittent power from grid-tied intermittent power generation systems during certain times of the day, sending it instead to energy storage devices, or to curtail the intermittent power generation systems during certain times of the day altogether.
Still another solution has been to give a utility centralized control over energy management controllers connected to customer circuits behind the utility meter to perform load shedding (decreasing load), load adding (increasing load), energy storage and energy export, as necessary, to manage the amount of energy exported to the grid from intermittent power generation systems. However, because of unpredictable and instantly changing intermittent power output on localized segments of a grid, customers' resistance to centralized utility control, communication delays between the controllers and the utility over distance, and other reasons, this is not a commercially viable solution.
Power factor correction is another problem for utilities (and other grid participants). By way of background, in a simple alternating current (AC) circuit consisting of an alternating current power source and a load, both the current and voltage are sinusoidal, that is, the electrical flow (current) and electrical pressure (voltage) alternate back and forth towards and away from the source, each in approximately a simple “sine” wave. If the load is purely resistive, such as in a light bulb or oven, then voltage and current remain in phase, and at every instant in a cycle, the product of voltage and current (which equals the electrical power) is positive (or zero once per cycle, when the current changes direction), indicating that only active power (or real power) is transferred (or no power is transferred once per cycle, when the current changes direction). Active power (or real power, measured in Watts) is the net power that is actually being used, or dissipated, in a circuit.
For current that flows toward the load and then returns to the source in a full AC cycle, there is no net transfer of energy, and no dissipation of real power. However, power is still needed to cause the current to flow back and forth, which is known as reactive power, which is measured in the unit of Volt-Ampere-Reactive to differentiate from real power). Put in another way, the portion of power that, over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as active power (sometimes also called real power). The portion of power which is sent out from the source and then returns to the source in each complete cycle is known as reactive power. The reactive power regulates the voltage in an AC power system, to provide enough voltage to move the active power through the system to the load. If the reactive power is too low, insufficient voltage is provided at the load. If the reactive power is too high, the system becomes overloaded. The need for excess reactive power wastes energy, reduces capacity and causes voltage fluctuations.
Inductive loads (loads that require current flowing through coils to create magnetic fields, such as transformers or motors) cause the sinusoidal wave of current to lag behind the sinusoidal wave of voltage, and capacitive loads (loads that involve charging devices with electricity) cause the sinusoidal wave of current to lead the sinusoidal wave of voltage. Inductive loads, capacitive loads, and other loads that cause the current to lead or lag the voltage, are called reactive loads. Causing the current to lead or lag the voltage causes the current to be “out of phase” with the voltage: current arrives at the wrong time to do work efficiently (either too early or too late), which increases the need for reactive power to move the active power.
Power factor is a measure of the efficiency of the power being used in an AC circuit and is the ratio of real power (measured in Watts (W)) to apparent power (the power that is supplied to the circuit, consisting of the sum of real power and reactive power, measured in Volt-Amperes (VA)). The power factor of a circuit is 1 when the voltage and current are in phase, and it is less than 1 when the current leads or lags the voltage, so they are out of phase—being out of phase creates reactive load. A high power factor at or near 1 is generally desirable in an electrical transmission system to reduce transmission losses and improve voltage regulation.
Loads at residential, commercial, industrial or other properties are typically a combination of resistive loads (heating devices) and inductive loads (motors and transformers), so that current usually lags behind voltage due to the inductive loads. Charging and discharging power storage devices, such as batteries, can create a capacitive load to help control power factor in these typical combinations.
Power factor correction brings the power factor of circuits closer to 1 by supplying reactive power of opposite sign, or by adding capacitive load (rechargeable battery systems), or by adding inductive load.
For example, to correct lagging power flow in a typical AC customer circuit with resistive and inductive loads, leading reactive power can be supplied to bring the current into phase with voltage. Or a capacitive load from battery charging can be added to help bring the current into phase with voltage. Inductive loads could also be turned off to reduce lagging power flow.
When the current is in phase with voltage, there is a reduction in transmission losses, an increase in system capacity, and a rise in voltage (preventing an undervoltage problem). Thus, reactive power can be supplied by a rechargeable battery storage system and can also be adjusted by turning on and off loads at a home.
The ability of the utility (or other grid participant) to accurately predict the reactive power (or other power characteristics) needed for intermediate circuits is critically important because providing too much or too little reactive power in electrical grids can lead to overvoltage or undervoltage conditions, and under certain operating conditions, to the complete collapse of the grid (blackout). An overvoltage or undervoltage condition is considered to be reached when the voltage rises above or lags below the nominal voltage by ten percent (10%) for more than 1 minute.
Utilities (or other grid participants) are, however, typically unaware of how much reactive power is required for individual customer circuits connected to an intermediate circuit because the utility (or other grid participant) usually cannot measure reactive power at a level lower than intermediate circuits, and especially behind customers' utility meters. Further, the reactive power for one customer on an intermediate, circuit may not have any relationship to the reactive power for any other customer on the same intermediate circuit. Accordingly, the utility for other grid participant) can only guess how much reactive power in the aggregate to supply to customers on an intermediate circuit.
The following patents and patent applications may be relevant to the field of the invention:
U.S. Pat. No. 8,855,829 B2 to Golden et al., incorporated herein by reference, discloses a system and method for managing power consumption and storage in a power grid. Measurements are received from a plurality of geographically distributed energy management controllers. Each energy management controller has energy storage units with stored energy. The measurements comprise the energy production and storage capacity of the energy management controllers and their associated energy storage units. The measurements are processed, for example aggregated and displayed on a graphical user interface. Commands are transmitted to a first subset of the energy management controllers to command the units to discharge their stored energy into a power grid through an inverter. Commands are transmitted to a second subset of the plurality of energy management controllers to store energy in each unit's energy storage unit.
U.S. Pat. No. 8,552,590 B2 to Moon et al., incorporated herein by reference, discloses an energy management system, including: a first interface configured to receive a first power from a power generation system; a second interface configured to couple to the power generation system, a power grid, and a storage device, and to receive at least one of the first power from the power generation system, a second power from the power grid, or a third power from the storage device, and to supply a fourth power to at least one of the power grid or a load; and a third interface configured to receive the third power from the storage device, and to supply a fifth power to the storage device for storage.
U.S. Patent Application Publication No. US 20130162215 A1 to Cooper, incorporated herein by reference, discloses a method of managing the consumption and distribution of electricity in a user facility, wherein the user facility is connected to an electricity supply grid and the user facility comprises a grid connected to an on-site generator; the method comprising the steps of measuring waveform conditions on a portion of the electricity supply grid adjacent the user facility to obtain locally measured waveform conditions; measuring electrical power readings from the on-site generator; communicating the locally measured waveform conditions and the electrical power readings to a controller in the user facility; determining, at least on the basis of the locally measured waveform conditions, whether the electricity supply grid is oversupplied or undersupplied with electricity; and, modifying the flow of the electricity within the user facility based on whether the electricity supply grid is oversupplied or undersupplied with electricity and/or the electrical power readings from the grid connected on site generator.
U.S. Pat. No. 8,558,991 B1 to Forbes. Jr., incorporated herein by reference, discloses systems, methods, and apparatus embodiments for electric power grid and network registration and management of active grid elements. Grid elements are transformed into active grid elements following initial registration of each grid element with the system, preferably through network-based communication between the grid elements and a coordinator, either in coordination with or outside of an IP-based communications network router. A multiplicity of active grid elements function in the grid for supply capacity, supply and/or load curtailment as supply or capacity. Also preferably, messaging is managed through a network by a Coordinator using IP messaging for communication with the grid elements, with the energy management system (EMS), and with the utilities, market participants, and/or grid operators.
U.S. Patent Application Publication No. US 20140018969 A1 to Joseph W. Forbes, Jr., incorporated herein by reference, discloses systems and methods for managing power supplied over an electric power grid by an electric utility and/or other market participants to a multiplicity of grid elements and devices for supply and/or load curtailment as supply, each of which having a Power Supply Value (PSV) associated with its energy consumption and/or reduction in consumption and/or supply, and wherein messaging is managed through a network by a Coordinator using IP messaging for communication with the grid elements and devices, with the energy management system (EMS), and with the utilities, market participants, and/or grid operators.
U.S. Pat. No. 8,457,802 B1 to Steven et al., incorporated herein by reference, discloses assisting customers in managing the four types of energy assets, that is, generation, storage, usage, and controllable load assets. Embodiments of the present invention for the first time develop and predict a customer baseline (“CBL”) usage of electricity, using a predictive model based on simulation of energy assets, based on business as usual (“BAU”) of the customer's facility. The customer is provided with options for operating schedules based on algorithms, which allow the customer to maximize the economic return on its generation assets, its storage assets, and its load control assets. Embodiments of the invention enable the grid to verify that the customer has taken action to control load in response to price. This embodiment of the invention calculates the amount of energy that the customer would have consumed, absent any reduction of use made in response to price. Specifically, the embodiment models the usage of all the customer's electricity consuming devices, based on the customer's usual conditions. This model of the expected consumption can then be compared to actual actions taken by the customer, and the resulting consumption levels, to verify that the customer has reduced consumption and is entitled to payment for the energy that was not consumed.
U.S. Patent Application Publication No. US 2011/0093127 A1 to Kaplan et al, incorporated herein by reference, discloses a Distributed Energy Resources Manager to connect electrical assets in an electricity distribution grid with other information-processing systems including, but not limited to, existing utility grid management systems to manage flows of information between electrical assets and interacting software assets and, thereby, manage performance of at least the electrical assets.